Hiding data in imagery or audio is a technique well known to artisans in the field, and is termed "steganography." There are a number of diverse approaches to, and applications of, steganography. A brief survey follows:
British patent publication 2,196,167 to Thorn EMI discloses a system in which an audio recording is electronically mixed with a marking signal indicative of the owner of the recording, where the combination is perceptually identical to the original. U.S. Pat. Nos. 4,963,998 and 5,079,648 disclose variants of this system.
U.S. Pat. No. 5,319,735 to Bolt, Berenak & Newman rests on the same principles as the earlier Thorn EMI publication, but additionally addresses psycho-acoustic masking issues.
U.S. Pat. Nos. 4,425,642, 4,425,661, 5,404,377 and 5,473,631 to Moses disclose various systems for imperceptibly embedding data into audio signals--the latter two patents particularly focusing on neural network implementations and perceptual coding details.
U.S. Pat. No. 4,943,973 to AT&T discloses a system employing spread spectrum techniques for adding a low level noise signal to other data to convey auxiliary data therewith. The patent is particularly illustrated in the context of transmitting network control signals along with digitized voice signals.
U.S. Pat. No. 5,161,210 to U.S. Philips discloses a system in which additional low-level quantization levels are defined on an audio signal to convey, e.g., a copy inhibit code, therewith.
U.S. Pat. No. 4,972,471 to Gross discloses a system intended to assist in the automated monitoring of audio (e.g. radio) signals for copyrighted materials by reference to identification signals subliminally embedded therein.
U.S. Pat. No. 5,243,423 to DeJean discloses a video steganography system which encodes digital data (e.g. program syndication verification, copyright marking, media research, closed captioning, or like data) onto randomly selected video lines. DeJean relies on television sync pulses to trigger a stored pseudo random sequence which is XORed with the digital data and combined with the video.
European application EP 581,317 discloses a system for redundantly marking images with multi-bit identification codes. Each "1" ("0") bit of the code is manifested as a slight increase (decrease) in pixel values around a plurality of spaced apart "signature points." Decoding proceeds by computing a difference between a suspect image and the original, unencoded image, and checking for pixel perturbations around the signature points.
PCT application WO 95/14289 describes the present applicant's prior work in this field.
Komatsu et al., describe an image marking technique in their paper "A Proposal on Digital Watermark in Document Image Communication and Its Application to Realizing a Signature," Electronics and Communications in Japan, Part 1, Vol. 73, No. 5, 1990, pp. 22-33. The work is somewhat difficult to follow but apparently results in a simple yes/no determination of whether the watermark is present in a suspect image (e.g. a 1 bit encoded message).
There is a large body of work regarding the embedding of digital information into video signals. Many perform the embedding in the non-visual portion of the signal such as in the vertical and horizontal blanking intervals, but others embed the information "in-band" (i.e. in the visible video signal itself). Examples include U.S. Pat. Nos. 4,528,588, 4,595,950, and 5,319,453; European application 441,702; and Matsui et. al, "Video-Steganography: How to Secretly Embed a Signature in a Picture," IMA Intellectual Property Project Proceedings, January 1994, Vol. 1, Issue 1, pp. 187-205.
There are various consortium research efforts underway in Europe on copyright marking of video and multimedia. A survey of techniques is found in "Access Control and Copyright Protection for Images (ACCOPI), WorkPackage 8: Watermarking," Jun. 30, 1995, 46 pages. A new project, termed TALISMAN, appears to extend certain of the ACCOPI work. Zhao and Koch, researchers active in these projects, provide a Web-based electronic media marking service known as Syscop.
Aura reviews many issues of steganography in his paper "Invisible Communication," Helskinki University of Technology, Digital Systems Laboratory, Nov. 5, 1995.
Sandford II, et al. review the operation of their May, 1994, image steganography program (BMPEMBED) in "The Data Embedding Method," SPIE Vol. 2615, Oct. 23, 1995, pp. 226-259.
A British company, Highwater FBI, Ltd., has introduced a software product which is said to imperceptibly embed identifying information into photographs and other graphical images. This technology is the subject of European patent applications 9400971.9 (filed Jan. 19, 1994), 9504221.2 (filed Mar. 2, 1995), and 9513790.7 (filed Jul. 3, 1995), the first of which has been laid open as PCT publication WO 95/20291.
Walter Bender at M.I.T. has done a variety of work in the field, as illustrate by his paper "Techniques for Data Hiding," Massachusetts Institute of Technology, Media Laboratory, January 1995.
Dice, Inc. of Palo Alto has developed an audio marking technology marketed under the name Argent. While a U.S. patent application is understood to be pending, it has not yet been issued.
Tirkel et al, at Monash University, have published a variety of papers on "electronic watermarking" including, e.g., "Electronic Water Mark," DICTA-93, Macquarie University, Sydney, Australia, December, 1993, pp.666-673, and "A Digital Watermark," IEEE International Conference on Image Processing, Nov. 13-16, 1994, pp. 86-90.
Cox et al, of the NEC Technical Research Institute, discuss various data embedding techniques in their published NEC technical report entitled "Secure Spread Spectrum Watermarking for Multimedia," December, 1995.
Moller et al. discuss an experimental system for imperceptibly embedding auxiliary data on an ISDN circuit in "Rechnergestutzte Steganographie: Wie sie Funktioniert und warum folglich jede Reglementierung von Verschlusselung unsinnig ist," DuD, Datenschutz und Datensicherung, 18/6 (1994) 318-326. The system randomly picks ISDN signal samples to modify, and suspends the auxiliary data transmission for signal samples which fall below a threshold.
There are a variety of shareware programs available on the internet (e.g. "Stego" and "White Noise Storm") which generally operate by swapping bits from a to-be-concealed message stream into the least significant bits of an image or audio signal. White Noise Storm effects a randomization of the data to enhance its concealment.